Sharing of the same inbound number is a common practice, especially with phone word (smart number) providers.
The way this works, is that an inbound number can be routed to multiple destination numbers. That means that for a single inbound number any calls from NSW callers could be routed to a number in Sydney, and for the same number, any calls from Victoria could be routed to a (different) Melbourne business. This allows phone word providers to lease the same number to different businesses in each state open.
Numbers can be routed right down to the exchange level, allowing a single 13, 1300 or 1800 number to be shared between multiple local businesses.